In the first case you are basing your belief on a capacity that within certain parameters (that is, in the right sort of environment) is an extremely reliable tree-detector (meaning it can detect real trees as opposed to fake trees, but not real trees as opposed to extremely vivid hallucinations). — Fafner

Why would you class all human beings together as "extremely reliable tree-detector"? What if all my life I've been calling shrubs by the name "tree"? Would you say that I'm an extremely reliable tree detector? How would you differentiate a shrub from a tree in an extremely reliable way?

I didn't say that having this sort of capacity is sufficient for knowledge, that's a different question. Obviously you have to be responsive in the right sort of way to the deliverances of you perception - I agree that not all instances of e.g. directly seeing a tree (de re) are instances of knowledge, but I don't see the relevancy here. — Fafner

The relevance is that simply having a veridical experience isn't enough to claim that one has knowledge of the external world. You need the periphery understanding that your experience is veridical, but that kind of understanding is impossible (according to the sceptic).

If you don't know that the tree you see is an external world tree then you don't know that there's an external world tree, even if the tree you see is an external world tree. Just as if I don't know that the blond woman I see is your mother then I don't know that your mother is blond, even if the blond woman I see is your mother.

The relevance is that simply having a veridical experience isn't enough to claim that one has knowledge of the external world. You need the periphery understanding that your experience is veridical, but that kind of understanding is impossible (according to the sceptic). — Michael

Again, we've been over this already. I don't know what you mean by "knowing that your experience is veridical". As it stands it just means nothing, and so it is no objection.

Again, we've been over this already. I don't know what you mean by "knowing that your experience is veridical". As it stands it just means nothing, and so it is no objection. — Fafner

It means knowing that the tree you see isn't just in your head. That you're not a brain in a vat or being deceived by an evil demon.

If you don't know that the tree you see is an external world tree then you don't know that there's an external world tree, even if the tree you see is an external world tree. Just as if I don't know that the blond woman I see is your mother then I don't know that your mother is blond, even if the blond woman I see is your mother. — Michael

On my account there's no difference between knowing that something is a tree and knowing that something is an "external world tree", so I don't understand what you mean.

It means knowing that the tree you see isn't just in your head. That you're not dreaming or imagining or a brain in a vat or being deceived by an evil demon. — Michael

You just repeated the world "know" here, but I asked what are the relevant conditions (according to the skeptic) for knowing such a thing? (which we allegedly fail to meet)

You just repeated the world "know" here, but I asked what are the relevant requirements (according to the skeptic) for knowing such a thing? — Fafner

Recognising some evidence as ruling out the possibility that you're wrong, as per your opening post. If I can't recognise some evidence as ruling out the possibility that the tree I see is just in my head – that I'm a brain in a vat or being deceived by an evil demon – then I don't know that the tree I see isn't just in my head.

Recognising some evidence as ruling out the possibility that you're wrong, as per your opening post. If I can't recognise some evidence as ruling out the possibility that the tree I see is just in my head – that I'm a brain in a vat or being deceived by an evil demon – then I don't know that the tree I see isn't just in my head. — Michael

You have to distinguish between two senses of recognizing your evidence: a. knowing that if you have evidence of type E then you cannot be a brain in a vat and b. infallibly knowing that you indeed have evidence E and not merely seeming to have them. I agree that knowing (a) is necessary for knowledge, but not knowing (b).

You have to distinguish between two senses of recognizing your evidence: a. knowing that if you have evidence of type E then you cannot be a brain in a vat and b. infallibly knowing that you indeed have evidence E and not merely seeming to have them. I agree that knowing (a) is necessary for knowledge, but not knowing (b). — Fafner

I know that if I have evidence that you have a sibling then you cannot be an only child. That doesn't mean that I know that you're not an only child. I need to actually have such evidence and recognise it for what it is. If I meet your brother but don't know that he's your brother then I don't know that you're not an only child.

Your conditional account of knowledge doesn't work. You need to actually have such evidence and recognise it for what it is. The problem is in recognising the evidence for what it is. How you do recognise that the experience you have is evidence that you're not a brain in a vat? The sceptic claims we can't.

I know that if I have evidence that you have a sibling then you cannot be an only child. That doesn't mean that I know that you're not an only child. I need to actually have such evidence and recognise it for what it is. If I meet your brother but don't know that he's your brother then I don't know that you're not an only child. — Michael

In that case, meeting my brother (or meeting my mother) is simply not an instance of you "having evidence that X is my brother/mother", because the conditional (a) doesn't hold here, and so it's not a counterexample (because you don't know that you've met my brother even if you did, while (a) says that if the event of "meeting my brother" is to be regarded as evidence for you that the guy is my brother, then you must antecendently know that the occurrence of the event of meeting that guy would entail the fact that you've met my brother - but in your story you don't know that. The point is that you don't have to suppose the stronger conditional (b) but (a) is sufficient to handle your stories).

Your conditional account of knowledge doesn't work. You need to actually have such evidence and recognise it for what it is. The problem is in recognising the evidence for what it is. How you do recognise that the experience you have is evidence that you're not a brain in a vat? The sceptic claims we can't. — Michael

I agree that you have to recognize that you indeed have the evidence when you do have them (and this is taken care of by (a)), but it doesn't follow that you capacity to recognize the evidence must be infallible.

If I'm seeing a tree in a waking state, and believe that I do, then I do recognize my evidence for what they are (and it's not a matter of coincidence). The question whether I can detect some possible cases of illusion is irrelevant to my ability to recognize the evidence in the veridical cases.

I don't see how you can make this conclusion. A person in a waking state may have poor eyes, poor judgement, or be hallucinating when thinking that they are in a state of perceiving a tree. — Metaphysician Undercover

I meant to exclude such cases, of course there are many ceteris paribus conditions that we must take into account. I meant that when you perceive a tree (you are not dreaming, your eyesight is normal etc.) then your perceptual state is correlated with the fact that there's a tree in front of you, and this is an objective matter. This is what should be properly regarded as your evidence.

You seem to be neglecting the fact that evidence must be judged. The person must judge the perceptual evidence, as well as the meaning of the statement "that is a tree", in order to know that that is a tree. Human judgements can be mistaken. Therefore the person can be wrong. — Metaphysician Undercover

My judgment is fallible, but it doesn't mean that my perceptual evidence is fallible, which is what I'm insisting on.

So here you use "objectively entail" to refer to the judgement which must be made. How do you ensure that the human judgement is not mistaken? — Metaphysician Undercover

No, it doesn't refer to my judgment. You know that p, if you judge that p on a basis of evidence which entails that p (and p is true). Such judgments are fallible as you say, but it doesn't show that they are not knowledge when they do succeeded.

I meant to exclude such cases, of course there are many ceteris paribus conditions that we must take into account. I meant that when you perceive a tree (you are not dreaming, your eyesight is normal etc.) then your perceptual state is correlated with the fact that there's a tree in front of you, and this is an objective matter. This is what should be properly regarded as your evidence. — Fafner

My point, is that the evidence, your perception of a tree, never provides the basis for a conclusion which beyond the possibility of doubt. If you exclude all the cases in which you were wrong, i.e. it turned out to be a shrub or something like that and not a tree, to support your claim that the judgement is beyond doubt, then you are being unrealistic.

No, it doesn't refer to my judgment. You know that p, if you judge that p on a basis of evidence which entails that p (and p is true). Such judgments are fallible as you say, but it doesn't show that they are not knowledge when they do succeeded. — Fafner

So you acknowledge that such judgements are fallible. If you make such a judgement then, one which you acknowledge as fallible, how would you know whether the judgement is mistaken or not. Since you cannot know such a thing, because all you have to go on is your judgement, and such judgements are fallible, then you cannot exclude doubt. Since "knowledge" as you use it refers to a successful judgement, and you have no way of knowing whether your judgement is successful or not, because you acknowledge that your judgement is fallible, then you have no way of knowing whether your judgements are knowledge or not. Therefore you should doubt all your knowledge.

My point, is that the evidence, your perception of a tree, never provides the basis for a conclusion which beyond the possibility of doubt. If you exclude all the cases in which you were wrong, i.e. it turned out to be a shrub or something like that and not a tree, to support your claim that the judgement is beyond doubt, then you are being unrealistic. — Metaphysician Undercover

It depends on what one means here by "evidence". On my understanding, having evidence for p is being in a state of such kind that you cannot be in this very same state when p is false. So when you perceive a tree in full daylight, your vision functions properly etc., then your visual experience of the tree is correlated with the fact that there is a tree (you cannot after all see a tree if there's no tree - of course you can mistakenly believe that you are seeing a tree, but the point is that if that happens then you're in a different kind of state).

Since "knowledge" as you use it refers to a successful judgement, and you have no way of knowing whether your judgement is successful or not, because you acknowledge that your judgement is fallible, then you have no way of knowing whether your judgements are knowledge or not. Therefore you should doubt all your knowledge. — Metaphysician Undercover

I think we should separate here the question about whether you know that p, and your degree of confidence in that knowledge (which I think are two different things). Indeed the thought that all our judgments are to some degree fallible may undermine our confidence in what we think we know (particularly when we think about the skeptical problem), but it doesn't have to. The skeptic says that our confidence in all of our claims to knowledge ought to be 0, since there are some crazy possibilities of error that we cannot rule out. But does it follow? I think not.

Think about it this way. Suppose that you are having an experience of seeing a tree in broad daylight etc., and also you don't have any particular reason to doubt that something is wrong with you - i.e., you don't remember taking drugs, or being told by the doctor that something is wrong with your eyesight and so on. Now, suppose that you form a belief that there's a tree in front of you on the basis of your experience. Is your belief entirely without grounds as the skeptic claims? I don't think so, because the experience that you are having does rule out objectively, some possibilities of error - e.g., that you are looking at a traffic light or a painting of a tree etc.- since it is impossible for a person with a normal eyesight and proper lighting conditions to take a painting or a traffic light for a real tree. So it is simply not true that your relying on the experience that you have (and given the background of your other beliefs) to be completely epistemically unjustified as if you've made a random guess (as the skeptic wants you to believe). Now, the skeptic will insist that there are some possibilities that your experience doesn't rule out - like for example you being a brain in a vat your whole life in a treeless world (which is true as I admitted). But the question is, why should we worry about such possibilities?. Suppose that (for some reason) you are confident that such a possibility is extremely unlikely and far fetched, and you just ignore it for all intents and purposes. Does it make you completely epistemically irresponsible or unreasonable? I think that no, since you are still very careful not to believe things which are plainly inconsistent with your actual experience - i.e. you don't form the belief that you are seeing a street light when you have an appearance of a tree etc., so you are objectivly excluding some possibilities of error, and you have excellent reasons to believe that.

So in pother words, what I'm trying to argue is that we have good grounds to trust our judgments (and take them to be knowledge) even in the face of their fallibility, since it is simply not the case that they are completely groundless. Why should we assess our judgments relative to the imaginary stories that the skeptic tells us? If we just stop being obsessive about absolute certainty, and adopt some more modest standards for knowledge claims (which is not the same as not having standards at all), then there will remain no longer any good reason to worry about what the skeptic is saying, and thus no reason to not to be confident in most of our claims to know.

If we just stop being obsessive about absolute certainty, and adopt some more modest standards for knowledge claims (which is not the same as not having standards at all), then there will remain no longer any good reason to worry about what the skeptic is saying, and thus no reason to not to be confident in most of our claims to know. — Fafner

The underlined portion of the quote is exactly what the (philosophical) skeptic is saying: that there is no absolute certainty, knowledge, or truth that we can apprehend, only optimal approximations of absolute certainty, absolute knowledge, or absolute truth - which is not the same as not having standards at all.

You seem to have answered the skeptic by coming full circle to what the skeptic is saying.

(BTW, skeptics such as Plato and Hume were not lacking in confidence.)

The underlined portion of the quote is exactly what the (philosophical) skeptic is saying: that there is no absolute certainty, knowledge, or truth that we can apprehend, only optimal approximations of absolute certainty, absolute knowledge, or absolute truth - which is not the same as not having standards at all. — javra

No, he doesn't say that - rather he's saying that there's no such thing as knowledge of the external world as such. See the conclusion of the skeptical argument in my first post. If what the skeptic was trying to prove is that absolutely certain knowledge is impossible, then that would not be a very interesting claim - but what makes his argument interesting is that he's claiming that there's no such thing as knowledge, no matter what standards of knowledge you adopt (that is, within the bounds of what we would be inclined to call 'knowledge').

No, he doesn't say that - rather he's saying that there's no such thing as knowledge of the external world as such. — Fafner

To found my statements in fact, both Plato and Hume held that there is an external world. Both were staunch philosophical skeptics, rather than parodies of what philosophical skepticism entails.

For me, that the skeptic claims there is no knowledge of the external world is a strawman. He/she might indeed agree that there is no absolute knowledge of an external world—but then, in another lampoonery of skepticism, he/she already claims that “I know [am aware] I know [as absolute truth] nothing – not even this”. [One can be charitable and not view what might have been intended through this statement to be a logical contradiction.]

I understand you have a different view. But, again, I look to people such as Plato and Hume to be the real thing when it comes to philosophical skepticism.

To found my statements in fact, both Plato and Hume held that there is an external world. Both were staunch philosophical skeptics, rather than parodies of what philosophical skepticism entails. — javra

Maybe you are right about Plato and Hume, but I'm not concerned with the views of any particular philosopher, but with a generic view (or rather a form of argument) which is called 'skepticism' in contemporary analytic philosophy (of course it doesn't mean that you cannot call other things 'skepticism', but that would be a different use of the world from the one that interests me in this thread).

Understood. I butted in in part due to me viewing this generic view which you address in you post to be, again, a pervasive misunderstanding (at best) of what is actually entailed by the given philosophical mindset. So, in a way, it seems like we might agree: namely, on our disagreement which the general stance that today goes by the name of "skepticism".

It depends on what one means here by "evidence". On my understanding, having evidence for p is being in a state of such kind that you cannot be in this very same state when p is false. — Fafner

That's a ridiculous definition of "evidence". Evidence supports a belief it does not render it impossible that the belief is false. That's why to convince someone of something it usually requires more than one piece of evidence. If evidence for a belief rendered the belief necessarily true, then all that would be required would be one piece of flimsy evidence and the belief would necessarily be true.

The skeptic says that our confidence in all of our claims to knowledge ought to be 0, since there are some crazy possibilities of error that we cannot rule out. But does it follow? I think not. — Fafner

I think you misunderstand skepticism. The skeptic doesn't claim that our confidence ought to be zero, the skeptic claims that the confidence cannot be one hundred percent. And, since we cannot have absolute, one hundred percent confidence in any claim of knowledge, all knowledge ought to be doubted.

Now, suppose that you form a belief that there's a tree in front of you on the basis of your experience. Is your belief entirely without grounds as the skeptic claims? — Fafner

Again, I think you misrepresent skepticism. The skeptic does not think that the belief is entirely without grounds, the skeptic thinks that the grounds for the belief ought to be examined. The skeptic doubts the belief on the assumption that the grounds for the belief may not be sound. So if I have been known to call trees shrubs before, or if I've called shrubs trees before, the skeptic wants to know this before assuming that my claim of a tree in front of me is a true claim.

I don't think so, because the experience that you are having does rule out objectively, some possibilities of error - e.g., that you are looking at a traffic light or a painting of a tree etc.- since it is impossible for a person with a normal eyesight and proper lighting conditions to take a painting or a traffic light for a real tree. — Fafner

But very often people mistake shrubs for trees, and trees for shrubs. It is a common mistake. A small tree might be mistook for a shrub, and a shrub might be mistook for a small tree. How do you rule out this possibility for error unless you know that the person is adept in this type of judgement?

So in pother words, what I'm trying to argue is that we have good grounds to trust our judgments (and take them to be knowledge) even in the face of their fallibility, since it is simply not the case that they are completely groundless. Why should we assess our judgments relative to the imaginary stories that the skeptic tells us? If we just stop being obsessive about absolute certainty, and adopt some more modest standards for knowledge claims (which is not the same as not having standards at all), then there will remain no longer any good reason to worry about what the skeptic is saying, and thus no reason to not to be confident in most of our claims to know. — Fafner

Skepticism is not a claim that knowledge is "completely groundless". It is the claim that the grounds are just as likely to be mistaken as anything else is. If the grounds for our judgements may be mistaken, then we ought assess these grounds, and judge them as well. This requires assessing and judging the grounds for those grounds, and on and on, until all the grounds have been assessed and judged. It is a matter of not taking anything for granted. If you take it for granted, that what you see is a tree, simply because you've been calling it a tree all your life, the day might come when someone explains to you that it's really a shrub. Then you might realize that you never really knew what it means to be a tree, when you just took it for granted that you did.

What would be the point in lowering the standards for knowledge? You seem to think that this would get rid of the skeptic, but actually the reverse is true. If the standards are lowered, we can say P is knowledge when we have a lower degree of certainty of P. This means more cases of what is called knowledge turning out to be false, giving us more reason to be skeptical of anything which is called knowledge.

See the conclusion of the skeptical argument in my first post. — Fafner

The argument concludes "no p can be known". It defines "know" as ruling out the possibility of error, in premise 1. The argument says nothing about degrees of confidence in one's belief. The skeptic doesn't say, as you claim, that we can have zero confidence, the skeptic says that if "knowing" requires ruling out the possibility of error, as per premise 1, then we cannot know anything. This does not say that we cannot have any confidence in our beliefs. It says something about the nature of "knowing".

That's a ridiculous definition of "evidence". Evidence supports a belief it does not render it impossible that the belief is false. That's why to convince someone of something it usually requires more than one piece of evidence. If evidence for a belief rendered the belief necessarily true, then all that would be required would be one piece of flimsy evidence and the belief would necessarily be true. — Metaphysician Undercover

Fine, if you don't like the definition, then you can weaken it, e.g., evidence is something that makes what is believed more probable or likely to be true than not - it doesn't change the main idea. What is crucial is that for something to be 'evidence' it must be intimately correlated with the facts that it is evidence for.

I think you misunderstand skepticism. The skeptic doesn't claim that our confidence ought to be zero, the skeptic claims that the confidence cannot be one hundred percent. And, since we cannot have absolute, one hundred percent confidence in any claim of knowledge, all knowledge ought to be doubted. — Metaphysician Undercover

If your grounds for claiming that you know something don't justify you to say that you know, then I think it comes down to the same thing as saying that you don't have any good reasons at all to say that you know (and hence you ought not to have any confidence in your knowledge whatsoever).

Again, I think you misrepresent skepticism. The skeptic does not think that the belief is entirely without grounds, the skeptic thinks that the grounds for the belief ought to be examined. — Metaphysician Undercover

If the belief is not entirely without grounds, then why are they not good enough to be considered knowledge? The structure of the skeptical argument is such that all of your claims to knowledge are completely worthless unless you've ruled out all possibilities of error. If he doesn't assume that, then it is simply not clear how all those sci-fi stories about deceiving demons and brains in a vat are supposed to prove skepticism (that we don't know that there's an external world etc.). Obviously the skeptics' argument is based on the idea that you can't say that you know something unless you are not absolutely sure that you are not mistaken - and of course this is the assumption that I'm rejecting.

But very often people mistake shrubs for trees, and trees for shrubs. It is a common mistake. A small tree might be mistook for a shrub, and a shrub might be mistook for a small tree. How do you rule out this possibility for error unless you know that the person is adept in this type of judgement? — Metaphysician Undercover

You rule it out by learning to identify shrubs, if they are very common where you live. Or alternatively, if you are living in an environment where there are no shrubs that look just like trees, then you can know that something is a tree without knowing anything about shrubs, or to be able to identify them. What are the relevant alternatives that one has to rule out is very much depend on the context.

Skepticism is not a claim that knowledge is "completely groundless". It is the claim that the grounds are just as likely to be mistaken as anything else is. — Metaphysician Undercover

Which is the same as saying that you have no grounds. If your grounds to believe that a certain event will happen are as good as your grounds to believe that the event will not happen, then you simply have no grounds whatsoever to believe either outcome (since for all you know, the probability is 50/50).

What would be the point in lowering the standards for knowledge? You seem to think that this would get rid of the skeptic, but actually the reverse is true. If the standards are lowered, we can say P is knowledge when we have a lower degree of certainty of P. This means more cases of what is called knowledge turning out to be false, giving us more reason to be skeptical of anything which is called knowledge. — Metaphysician Undercover

I think that no person in the world actually believes that he's infallible like God, so 'lowering the standards for knowledge' simply means adopting the standards that all reasonable people adopt anyway, so this ought no to be a problem.

The argument concludes "no p can be known". It defines "know" as ruling out the possibility of error, in premise 1. The argument says nothing about degrees of confidence in one's belief. The skeptic doesn't say, as you claim, that we can have zero confidence, the skeptic says that if "knowing" requires ruling out the possibility of error, as per premise 1, then we cannot know anything. This does not say that we cannot have any confidence in our beliefs. It says something about the nature of "knowing". — Metaphysician Undercover

I should qualify that by 'confidence' I meant 'justified confidence' in the epistemic sense. Of course the skeptic doesn't dispute that most people, as a matter of psychological fact, are confident that they know many things; his claim is rather that they ought not to be confident in that, because they don't really know anything, properly speaking. And my response was to claim that we actually do have much better reasons to be confident in our beliefs than what the skeptic thinks (and recall that it was a response to what you argued in your previous post, that since all our judgments are fallible, we can't know that what we have is knowledge, and I tried to show that it doesn't follow).

What is crucial is that for something to be 'evidence' it must be intimately correlated with the facts that it is evidence for. — Fafner

No, evidence is apprehended as being correlated with the belief which it is evidence for. So you have two things wrong here. First, the thing which the evidence is evidence of, is a belief it is not a fact. It cannot be called a fact, because the purpose of evidence is to convince someone of something which may or may not be true. Second, in order for it to be called evidence, it need not be intimately related to the belief, it needs only to be perceived as such. This is what makes it evidence of the thing, the fact that it is perceived as being related to the thing, whether or not it actually is, is irrelevant.

If your grounds for claiming that you know something don't justify you to say that you know, then I think it comes down to the same thing as saying that you don't have any good reasons at all to say that you know (and hence you ought not to have any confidence in your knowledge whatsoever). — Fafner

This doesn't make any sense to me. You seem to be using "justify" in a strange way. We often claim to know something when someone we trust has told us that. But this is not at all a form of justification. So we often claim to know something, and have a reason for making such a claim, yet that reason doesn't constitute justification.

The structure of the skeptical argument is such that all of your claims to knowledge are completely worthless unless you've ruled out all possibilities of error. — Fafner

I've already told you, as well as javra has told you, that this is a misrepresentation of skepticism. In my last post, I clearly pointed out, in your own argument, how what you say here is not true to your argument.

Obviously the skeptics' argument is based on the idea that you can't say that you know something unless you are not absolutely sure that you are not mistaken - and of course this is the assumption that I'm rejecting. — Fafner

The argument, as you presented it, is that if knowing something requires absolute certainty, then we do not know anything. It does not say that you cannot know anything unless you are absolutely certain.

No, evidence is apprehended as being correlated with the belief which it is evidence for. So you have two things wrong here. First, the thing which the evidence is evidence of, is a belief it is not a fact. It cannot be called a fact, because the purpose of evidence is to convince someone of something which may or may not be true. Second, in order for it to be called evidence, it need not be intimately related to the belief, it needs only to be perceived as such. This is what makes it evidence of the thing, the fact that it is perceived as being related to the thing, whether or not it actually is, is irrelevant. — Metaphysician Undercover

I think I take the ground being wet as evidence that it rained recently because rain makes the ground wet.

How do you describe this scenario?

You have a belief that it rained recently. This belief is supported by your perception that the ground is wet, along with a logical principle such as "if the ground is wet, then it has rained recently", or as you say, "rain makes the ground wet". It is the assumption of this logical principle which makes your perception of the ground being wet into evidence of "it rained recently".

The strength of the evidence depends on the strength of the logical principle. "Rain makes the ground wet" is rather weak because there are other things which could make the ground wet as well. So we'd have to resort to probabilities, or other evidence to make a conclusive decision. "If the ground is wet, then it has rained recently" is a much stronger principle, but it is not true, because there are other things which could make the ground wet. So strengthening the logical principle may create the appearance of strengthening the evidence, but if this renders the logical principle unsound, then the evidence may be completely dismissed.

No, evidence is apprehended as being correlated with the belief which it is evidence for. So you have two things wrong here. First, the thing which the evidence is evidence of, is a belief it is not a fact. It cannot be called a fact, because the purpose of evidence is to convince someone of something which may or may not be true. Second, in order for it to be called evidence, it need not be intimately related to the belief, it needs only to be perceived as such. This is what makes it evidence of the thing, the fact that it is perceived as being related to the thing, whether or not it actually is, is irrelevant. — Metaphysician Undercover

Evidence is connected to belief via its relation to the facts. One usually believes that such and such is the case because the evidence tells him that such and such is the case. If the evidence didn't indicate anything about how things are in the world, it would make no sense to believe things on their basis. If you didn't believe that e.g., having an experience of seeing a tree is somehow connected with the presence of trees, then you would not take your experience as grounds to believe that there's a tree.

This doesn't make any sense to me. You seem to be using "justify" in a strange way. We often claim to know something when someone we trust has told us that. But this is not at all a form of justification. So we often claim to know something, and have a reason for making such a claim, yet that reason doesn't constitute justification. — Metaphysician Undercover

I don't understand what you are saying. If you are not justified to believe p on the basis of E, then E is not a justification, or a bad justification, or a bad reason (however you want to call it) to believe that p. You can't have it both ways. It's nonsense to say that you have good reasons to believe that p but you are not justified to do so, or vice versa (and I'm treating here 'reasons' 'grounds' and 'justification' interchangeably).

I've already told you, as well as javra has told you, that this is a misrepresentation of skepticism. In my last post, I clearly pointed out, in your own argument, how what you say here is not true to your argument. — Metaphysician Undercover

But you have said this very thing yourself in one of your earlier comments, quote: " because you acknowledge that your judgement is fallible, then you have no way of knowing whether your judgements are knowledge or not. Therefore you should doubt all your knowledge", which comes to the same as saying that one doesn't have grounds or justifications to claim that one knows something, which is precisely what I said.

The argument, as you presented it, is that if knowing something requires absolute certainty, then we do not know anything. It does not say that you cannot know anything unless you are absolutely certain. — Metaphysician Undercover

How come? It follows logically...

If S knows p only when S is certain that p - then, the conjunction that S knows that p and S is not certain that p is always false (that is, necessarily false).

If P -> Q

then it is not the case that P & ~Q.

Simple logic.

[

2. Waking experience is indistinguishable from a very vivid dream (or a deception by an evil demon, or being a brain in a vat etc. – insert here your favorite skeptical scenario), since there are no distinct "marks" to distinguish the one from the other. — Fafner

I don't know if this has been brought up, but anyway here it goes.
What causes you to have experiences?
What can you control?

These are the 2 key questions in trying to answer if you can differentiate between P and non-P. So I will use my favorite combinations of skeptical scenarios. A Boltzmann brain and a brain in a vat. Imagine a universe where the universe is your brain and the machinery, needed biological matter, computer, power supply and so on to run you as a brain in vat.
Notes - the Boltzmann brain part is that the universe you are in, came to existence as only being a universe with you as a brain in a vat. That is what your universe is.

So now enter causation and control for the following 2 kinds of universes:
The universe you use P for and the Boltzmann brain universe as non-P.
Now you ask yourself this:
Have both universes caused me to come into existence?
Do both universes cause me to have the same experiences?
Can I cause(control) the universe I am in to be the P-universe by thinking/reasoning that it is the P-universe?
Can I step outside either universe to check which one I am in?

My point is that you can't neither know what universe caused to have your experiences, you can't check it and you can't cause the universe to be the one you want it to be by you reasoning/thinking. Reasoning/thinking is caused by whatever universe you are in.

The answer is that knowing about the world is not a matter of knowing what causes your beliefs/experiences. It is true that (as a matter of scientific fact) we have experiences because of the causal impingement of the world on our senses, but it doesn't follow that we have to know anything about those causal processes to have knowledge about the world.

You take for granted that we can know about the world. I don't, because I haven't been able to find any knowledge about the world, which isn't either a tautology or not knowledge, because it runs into Agrippa's trilemma.
You are begging the question if you start with the assumption that we have non-tautological knowledge about the world.
What you have in my belief system is experiences about the world and the belief that these experiences match what they imply. I hold the same belief; i.e. e.g. that there is a computer screen in front of me, but I don't know that. I just believe it.

So I take for granted that you believe that when you read this, there is some form of medium through which you have an experience of "reading"; e.g you might be dyslexic and "read" through have this text read aloud.
So what caused you to have the experience of read this text?
Are you seriously going to throw out causation and claim it is irrelevant for the world?
Again, what caused you to have an experiences of reading this text and how do you know that? You claim knowledge about the world, so you must know this.

It only begs-the-question if you believe that propositions like "I live on the earth" or "I am a person," need some kind of justification. What I believe to be the case, is that certain statements are bedrock to the whole of our epistemic system, and this is what Descartes didn't understand, viz., that justification comes to an end. At some point it just doesn't make sense to epistemically doubt that there is no difference between, for example, dreams and waking states. The argument seems to grant that there is a difference on the one hand, but then they take it away on the other hand to shore up the argument. There is something very fundamental about our perceptions that's generally grounded for us, i.e., we generally accept them as veridical without the need for justification.

It only begs-the-question if you believe that propositions like "I live on the earth" or "I am a person," need some kind of justification — Sam26

I don't think that they need some kind of justification. I think that a realist interpretation of such claims needs some kind of justification.

At some point it just doesn't make sense to epistemically doubt that there is no difference between, for example, dreams and waking states.

I accept that there is a difference. The issue is on the nature of that difference. Are they different just in terms of quality, or are they different in such a way that waking states conform to realist metaphysics?

There is something very fundamental about our perceptions that's generally grounded for us, i.e., we generally accept them as veridical without the need for justification.

Yes, we do, but it doesn't follow from that that we're right. You're welcome to just commit to this acceptance and carry on with your life, but that hardly counts as a good philosophical defence of the position against alternatives (anti-realism, idealism, phenomenalism, etc.).

Sorry, im confused by the original post

Does one's working definitions of Waking and Dreaming reduce to immediate empirical contents, to non-immediate empirical implications, to both or to neither?

Do the sets of experiences referred to by one's working definition of waking and dreaming overlap, or do waking and dreaming refer to disjoint sets of experiences?